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Abstract:

An abrasive article including an abrasive body having abrasive grains
made of microcrystalline alumina contained within a bond material,
wherein the bond material comprises a total content of alumina of at
least about 15 mol %.

Claims:

1. An abrasive article comprising: an abrasive body having abrasive
grains comprising microcrystalline alumina contained within a bond
material, wherein the bond material comprises a total content of alumina
of at least about 15 mol %.

2. The abrasive article of claim 1, wherein the total content of alumina
is at least about 15.5 mol %.

3-4. (canceled)

5. The abrasive article of claim 1, wherein the total content of alumina
is within a range between about 15 mol % and about 25 mol %.

16. The abrasive article of claim 1, wherein the microcrystalline alumina
comprises crystallites having an average crystallite size of less than
about 1 micron.

17-18. (canceled)

19. An abrasive article comprising: an abrasive body having abrasive
grains comprising microcrystalline alumina contained within a vitreous
bond material, wherein the vitreous bond material comprises a total
content of alumina [C.sub.Al2O3] in mol % of at least about 15 mol %, and
further comprises a total content of silica [C.sub.SiO2] in mol %, the
vitreous bond material having a ratio of [C.sub.Al2O3]/[C.sub.SiO2] of at
least about 0.2.

20. The abrasive article of claim 19, wherein the ratio of
.sub.[C.sub.Al2O3]/[C.sub.SiO2] is at least about 0.3.

21. (canceled)

22. The abrasive article of claim 19, wherein the ratio of
[C.sub.Al2O3]/[C.sub.SiO2] is within a range between about 0.2 and about
1.

23-24. (canceled)

25. The abrasive article of claim 19, wherein the abrasive body comprises
at least about 34 vol % abrasive grains of the entire volume of the
abrasive body.

26-30. (canceled)

31. The abrasive article of claim 19, wherein the abrasive body comprises
between about 4 vol % and about 30 vol % bond material of the entire
volume of the abrasive body.

32-40. (canceled)

41. An abrasive article comprising: an abrasive body having abrasive
grains comprising microcrystalline alumina contained within a vitreous
bond material, wherein the vitreous bond material comprises a total
content of alumina [C.sub.Al2O3] of at least about 15 mol %, a total
content of silica [C.sub.SiO2] of not greater than about 70 mol %, and a
total content of alkali oxide compounds [Caoc] selected from the
group of alkali compounds consisting of potassium oxide (K2O),
sodium oxide (Na2O), and lithium oxide (Li2O) is not greater
than about 15 mol %.

42. The abrasive article of claim 41, wherein the total content of silica
is not greater than about 65 mol %.

43-45. (canceled)

46. The abrasive article of claim 41, wherein the total content of alkali
oxide compounds is not greater than about 12 mol %.

47-48. (canceled)

49. The abrasive article of claim 41, wherein the total content of alkali
oxide compounds is within a range between about 1.0 mol % and about 15
mol %.

50-51. (canceled)

52. The abrasive article of claim 41, wherein the content of sodium oxide
is greater than the total content of potassium oxide and lithium oxide
combined.

53-55. (canceled)

56. The abrasive article of claim 41, wherein the vitreous bond material
comprises a total content of boron oxide of at least about 5.0 mol %.

57-61. (canceled)

62. The abrasive article of claim 56, wherein the vitreous bond material
comprises a ratio between the total content of alumina [C.sub.Al2O3] and
the total content of boron oxide [C.sub.B2O3], described as
[C.sub.Al2O3]/[C.sub.B2O3] within a range between about 0.2 and about 2.

[0005] Abrasive tools are generally formed to have abrasive grains
contained within a bond material for material removal applications.
Superabrasive grains (e.g., diamond or cubic boron nitride (CBN)) or
seeded (or even unseeded) sintered sol gel alumina abrasive grain, also
referred to microcrystalline alpha-alumina (MCA) abrasive grain, can be
employed in such abrasive tools and are known to provide superior
grinding performance on a variety of materials. The bond material can be
organic materials, such as a resin, or an inorganic material, such as a
glass or vitrified material. In particular, bonded abrasive tools using a
vitrified bond material and containing MCA grains or superabrasive grain
are commercially useful for grinding precision metal parts and other
industrial components requiring consistent and improved grinding
performance.

[0006] Certain bonded abrasive tools, particularly those utilizing a
vitrified bond material, require high temperature forming processes,
which can have deleterious effects on the abrasive grains. In fact, it
has been recognized that at such elevated temperatures necessary to form
the abrasive tool, the bond material can react with the abrasive grains,
particularly MCA grains, damaging the integrity of the abrasive, and
reducing the grain sharpness and performance properties. As a result, the
industry has migrated toward reducing the formation temperatures
necessary to form the bond material in order to curb the high temperature
degradation of the abrasive grains during the forming process.

[0007] For example, to reduce the amount of reaction between MCA grain and
vitrified bond, U.S. Pat. No. 4,543,107 discloses a bond composition
suitable for firing at a temperature as low as about 900° C. In an
alternate approach, U.S. Pat. No. 4,898,597 discloses a bond composition
comprising at least 40% fritted materials suitable for low firing
temperature vitreous bonds. Other such bonded abrasive articles utilizing
bond materials capable of forming at temperatures below 1100° C.,
and in fact, below 1000° C., include U.S. Pat. No. 5,203,886, U.S.
Pat. No. 5,401,284, U.S. Pat. No. 5,536,283, and U.S. Pat. No. 6,702,867.
Still, the industry continues to demand improved performance of such
bonded abrasive articles.

SUMMARY

[0008] According to one aspect, an abrasive article includes an abrasive
body having abrasive grains comprising microcrystalline alumina contained
within a bond material, wherein the bond material has a total content of
alumina of at least about 15 mol %.

[0009] According to another aspect, an abrasive article includes an
abrasive body having abrasive grains made of microcrystalline alumina
contained within a vitreous bond material, wherein the vitreous bond
material comprises a total content of alumina [C.sub.Al2O3] in mol % of
at least about 15 mol %. The vitreous bond material further comprises a
total content of silica [C.sub.SiO2] in mol %, the vitreous bond material
having a ratio of [C.sub.Al2O3]/[C.sub.SiO2] of at least about 0.2.

[0010] In another aspect an abrasive article includes an abrasive body
having abrasive grains made of microcrystalline alumina contained within
a vitreous bond material, wherein the vitreous bond material comprises a
total content of alumina [C.sub.Al2O3] of at least about 15 mol %, a
total content of silica [C.sub.SiO2] of not greater than about 70 mol %,
and a total content of alkali oxide compounds [Caoc] selected from
the group of alkali compounds consisting of potassium oxide (K2O),
sodium oxide (Na2O), and lithium oxide (Li2O) is not greater
than about 15 mol %.

[0011] According to still another aspect, an abrasive article includes an
abrasive body having abrasive grains comprising microcrystalline alumina
contained within a vitreous bond material, wherein the vitreous bond
material comprises a grain dissolution factor of not greater than about
1.0 wt %.

[0012] In yet another aspect, an abrasive article includes an abrasive
body having abrasive grains comprising microcrystalline alumina contained
within a vitreous bond material, wherein the vitreous bond material is
formed from a powder bond material having a sufficient amount of alumina
to reduce the dissolution of the abrasive grains as measured by a change
in total alumina content [Δ Al2O3] between the alumina
content of the powder bond material [PBM.sub.Al2O3] and the total alumina
content of the vitreous bond material [VBM.sub.Al2O3] of not greater than
about 15.0 mol % as calculated by the equation

[Δ Al2O3]=([VBM.sub.Al2O3-PBM.sub.Al2O3]/[PBM.sub.Al2O3]-
.

[0013] According to one aspect, a method of forming an abrasive article
includes mixing abrasive grains comprising microcrystalline alumina with
a bond material powder, wherein the bond material powder comprises at
least about 15 mol % alumina, and forming the mixture into a green
article. The method further includes heating the green article to a
firing temperature of at least about 800° C. to form an abrasive
article having abrasive grains contained within a vitreous bond material.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The present disclosure may be better understood, and its numerous
features and advantages made apparent to those skilled in the art by
referencing the accompanying drawings.

[0015]FIG. 1 includes a flow chart illustrating a method of forming an
abrasive article in accordance with an embodiment.

[0016]FIG. 2 includes a plot of power consumption versus number of
grinding cycles for a sample formed according to an embodiment and a
conventional sample.

[0017]FIG. 3 includes a plot of straightness versus number of grinding
cycles for a sample formed according to an embodiment and a conventional
sample.

[0018] The use of the same reference symbols in different drawings
indicates similar or identical items.

DETAILED DESCRIPTION

[0019] The following is generally directed to an abrasive article,
particularly a bonded abrasive article utilizing abrasive grains
contained within a bond material. Such abrasive articles are useful in
material removal applications, such as those in various industries for
finishing and/or grinding workpieces. The abrasive articles can be shaped
and sized to make various finishing tools, such as wheels, cones,
cup-shaped articles, hones, and/or stones.

[0020]FIG. 1 includes a flow chart illustrating a method of forming an
abrasive article in accordance with an embodiment. As illustrated, the
process is initiated at step 101 by mixing abrasive grains with a bond
material powder. In accordance with an embodiment, the abrasive grains
can include an inorganic material, such as an oxide. More particularly,
the abrasive grains can include microcrystalline alumina (MCA) grains.

[0021] The MCA or sol-gel alumina grains are preferably produced by either
a seeded or an unseeded sol-gel process. As used herein, the term
"sol-gel alumina grits" are alumina grits made by a process comprising
peptizing a sol of an aluminum oxide monohydrate so as to form a gel,
drying and firing the gel to sinter it, and then breaking, screening, and
sizing the sintered gel to form polycrystalline grains made of alpha
alumina microcrystals (e.g., at least about 95% alumina). In addition to
the alpha alumina microcrystals, the initial sol may further include up
to 15% by weight of spinel, mullite, manganese dioxide, titania,
magnesia, rare earth metal oxides, zirconia powder or a zirconia
precursor (which can be added in larger amounts, e.g. 40 wt % or more),
or other compatible additives or precursors thereof. These additives are
often included to modify such properties as fracture toughness, hardness,
friability, fracture mechanics, or drying behavior. Preparation of
sintered sol gel alpha-alumina grains is described in detail elsewhere.
Details of such preparations may be found, for example, in U.S. Pat. Nos.
4,623,364, 4,314,827, and 5,863,308, the contents of which are hereby
incorporated by reference.

[0022] The term MCA grain is defined to include any grain comprising at
least 60% alpha alumina microcrystals having at least 95% theoretical
density and a Vickers hardness (500 grams) of at least 18 GPa at 500
grams. The sintered sol gel alpha-alumina grain may contain platelets of
material other than alpha-alumina dispersed among the alpha-alumina
microcrystals. Generally, the alpha-alumina particles and the platelets
are submicron in size when made in this form. Further details of MCA
abrasive grain preparations and MCA abrasive grain types useful in the
present invention may be found in any one of the numerous other patents
and publications, which cite the basic technology disclosed in the U.S.
Pat. Nos. 4,623,364 and 4,314,827.

[0023] The microcrystalline alumina utilized in the abrasive grains can
have an average crystallite size of less than 1 micron. In fact, in
certain instances, the microcrystalline alumina can have an average
crystallite size of less than about 0.5 microns, and particularly within
a range between about 0.1 and about 0.2 microns.

[0024] Additionally, it will be appreciated that the bonded abrasive
articles of embodiments herein may utilize a certain content of secondary
abrasive grains. When secondary abrasive grains are used, such abrasive
grains can provide from about 0.1 to about 97 vol % of the total abrasive
grain of the tool, and more preferably, from about 30 to about 70 vol %.
The secondary abrasive grains which may be used include, but are not
limited to, alumina oxide, silicon carbide, cubic boron nitride, diamond,
flint and garnet grains, and combinations thereof. As such, certain
abrasive articles herein may utilize a mixture of abrasive grains such
that the abrasive article comprises a first portion of abrasive grains
made of MCA and a second portion of abrasive grains selected from the
group of materials consisting of superabrasive grains, monocrystalline
alumina, and a combination thereof.

[0025] In reference to the bond material powder, inorganic materials may
be utilized, and in particular, inorganic materials that facilitate the
formation of a final-formed abrasive article having a vitreous bond. That
is, the final-formed bonded abrasive article can have a vitreous bond
having a certain content of amorphous phase. In particular, the
final-formed bonded abrasive article of embodiments herein can have a
bond material that consists essentially of an amorphous phase.

[0026] In particular instances, the bond material powder can include
inorganic materials, such as oxides. Notably, the bond material powder
can include a frit material that is suitable for forming the final-formed
vitreous bond material. A frit material can include a powder material
formed form a glass, which is formed by firing initially to an elevated
temperature (e.g., 1000° C. or greater), cooling, crushing and
sizing to yield a powdered material ("a frit"). The frit then may be
melted at a temperature well below the initial firing temperature used to
make the glass from the raw materials, such as silica and clays.

[0027] The following paragraphs denote certain contents and certain
compositions, which may be used in the bond material powder, otherwise
the initial mixture of bond components. It will be appreciated that
reference herein to the particular amounts of certain compositions in
forming the mixture may not necessarily form a final vitreous bond
material in the abrasive article having the exact same composition of the
initial bond material powder. Particularly, the amount of certain oxide
compounds present in the final vitreous bond material may be different
than the amount of the same oxide compound present within the initial
bond material powder, while the amount of other oxide components may
remain substantially unchanged.

[0028] Embodiments herein can utilize a bond material powder having a frit
material. The frit material may be formed from oxides such as silica,
alkaline oxide compounds, alkaline earth oxide compounds, and a
combination thereof. The frit material facilitates suitable forming of a
vitrified bond material in the final-formed bonded abrasive. The frit
material can be provided in an amount of up to 100% of the bond material
powder, such that the bond material powder is comprised only of frit
material, however, in particular instances the bond material powder can
contain between about 10 wt % and about 60 wt % of frit material for the
total weight of the bond material powder.

[0029] According to one embodiment, the bond material powder can include a
certain content of silica (SiO2). For example, embodiments herein
may utilize a bond material powder formed from at least about 35 mol %
silica. In other embodiments, the amount of silica can be greater, such
as at least about 40 mol %, such as at least about 45 mol %, and
particularly within a range between about 35 mol % and about 60 mol %
silica, such as between about 40 mol % and about 55 mol %.

[0030] The frit material may also contain a particular content of
materials, including for example, aluminum oxide (i.e., alumina).
Provision of a frit material having a particular content of alumina may
facilitate formation of a first liquid phase during the thermal treatment
that is enriched with alumina, which may limit dissolution of the
abrasive grains by the first liquid phase. Particularly suitable contents
of alumina within the frit material can include at least about 20 mol %,
such as at least about 25 mol %, at least about 30 mol %, at least about
40 mol %, or even at least about 50 mol % of the total moles of frit
material. Still, the total amount of alumina may be limited, for example,
within a range between about 20 mol % and about 75 mol %, such as between
about 20 mol % and about 65 mol %, or even between about 20 mol % and
about 50 mol %.

[0031] Additionally, the final-formed bond material can be formed from a
bond material powder having a certain content of alkali oxide compounds.
Alkali oxide compounds are oxide compounds and/or complexes utilizing
alkali species denoted as Group 1A elements in the Periodic Table, such
as lithium oxide (Li2O), potassium oxide (K2O), sodium oxide
(Na2O), cesium oxide (Cs2O), and a combination thereof.

[0032] In accordance with one embodiment, the bond material powder can be
formed from not greater than about 18 mol % total alkali oxide compounds.
In other instances, the bond material powder is formed from less alkali
oxide compounds, such as on the order of not greater than about 16 mol %,
not greater than about 15 mol %, not greater than about 12 mol %, not
greater than about 10 mol %, or even not greater than about 8.0 mol % of
the total moles of the bond material powder. Particular embodiments
herein may form a bond material powder having a total content of alkali
oxide compounds within a range between about 2.0 mol % and about 18 mol
%, such as between about 5.0 mol % and about 16 mol %, between about 8.0
mol % and about 15 mol %, and even between about 8.0 mol % and about 12
mol %.

[0033] The bond material powder can contain a particularly low content of
lithium oxide, which may be more prevalent in certain low-temperature
bond compositions. For example, in certain embodiments, the bond material
powder can be formed from less than 8.0 mol % lithium oxide, such as less
than about 6.0 mol % lithium oxide, less than about 5.0 mol % lithium
oxide, and even less than about 4.0 mol % lithium oxide of the total
moles of the bond material powder. Particular embodiments may utilize an
amount of lithium oxide within a range between about 1.0 mol % and about
8.0 mol %, such as between about 2.0 mol % and about 6.0 mol %, or even
between about 3.0 mol % and about 6.0 mol %.

[0034] The bond material powder can be formed from a particular content of
potassium oxide, which can be less than a content of any other alkali
oxide material as measured in mol %. In fact, certain bond material
powder compositions may contain an amount of potassium oxide of not
greater than about 6.0 mol %, such as on the order of not greater than
about 5.0 mol %, not greater than about 4.0 mol %, or even not greater
than about 3.0 mol % of the total moles of the bond material powder.
Still, the bond material powder can be formed from an amount of potassium
oxide within a range between about 0.01 mol % and about 6.0 mol %, such
as between about 0.1 mol % and about 5.0 mol %, and even between about
0.2 mol % and about 5.0 mol %.

[0035] The bond material powder can be formed from a particular content of
sodium oxide. Notably, the content of sodium oxide may be greater than
the amount of any other individual alkali oxide compound, such as
potassium oxide or lithium oxide. In certain bond material powder
compositions, the amount of sodium oxide is at least 2 times greater than
the amount of potassium oxide or lithium oxide. Other bond material
powder compositions can have at least about 3 times greater sodium oxide,
at least 4 times greater, and particularly between about 2 times greater
and about 5 time greater amount of sodium oxide than potassium oxide or
lithium oxide.

[0036] For certain embodiments, the bond material powder can be formed
from at least about 6.0 mol % sodium oxide of the total moles of the bond
material powder. In other instances, the bond material powder can be
formed from at least about 8.0 mol %, at least about 10 mol %, at least
about 12 mol %, or eve at least about 14 mol % sodium oxide. Certain bond
material powders contain an amount of sodium oxide within a range between
about 6.0 mol % and about 18 mol %, such as between about 8.0 mol % and
about 16 mol %, such as between about 10 mol % and about 15 mol %.

[0037] The final vitreous bond material can be formed from a bond material
powder, which can be formed from a certain content of alkaline earth
oxide compounds. Alkaline earth oxide compounds are oxide compounds and
complexes incorporating divalent species from the alkaline earth elements
present in Group 2A of the Periodic Table of Elements. That is, for
example, suitable alkaline earth oxide compounds can include magnesium
oxide (MgO), calcium oxide (CaO), strontium oxide (SrO), barium oxide
(BaO), and a combination thereof.

[0038] In accordance with one embodiment, the bond material powder used
can be formed from not greater than about 15 mol % total alkaline earth
oxide compounds of the total moles of the bond material powder. In other
instances, the content of alkaline earth oxide compounds is less, such as
on the order of not greater than about 12 mol %, not greater than about
10 mol %, not greater than about 8.0 mol %, not greater than about 6.0
mol %, not greater than about 5.0 mol %, or even not greater than about
4.0 mol %. Particular embodiments herein may utilize a total content of
alkaline earth oxide compounds within a range between about 0.05 mol %
and about 15 mol %, such as between about 0.1 mol % and about 12 mol %,
between about 0.1 mol % and about 10 mol %, between about 0.1 mol % and
about 8.0 mol %, and even between about 0.5 mol % and about 5.0 mol %.

[0039] Of the alkaline earth oxide compounds, magnesium oxide may be
present in the greatest content as compared to the other alkaline earth
oxide compounds for certain bond material powder compositions. For
example, a sufficient amount of magnesium oxide within the bond material
powder can include at least about 0.5 mol %, such as at least 1.0 mol %,
at least about 1.5 mol % magnesium oxide, and particularly between about
0.5 mol % and about 5.0 mol %, or between about 0.5 mol % and about 3.0
mol % of the total moles of the bond material powder. Still, certain bond
material powder compositions can be essentially free of magnesium oxide.

[0040] The bond material powder can include a certain content of calcium
oxide. In particular, the content of calcium oxide can be less than the
content of magnesium oxide, but this may not necessarily be the case for
all bond material powder compositions. For example, embodiments herein
may utilize a bond material powder formed from not greater than about 5.0
mol %, such as not greater than about 3.0 mol %, not greater than about
2.0 mol %, or even not greater than about 1.0 mol % calcium oxide of the
total moles of the bond material powder. Particular mixes of the bond
material powder can be formed from between about 0.01 mol % and about 5.0
mol %, such as between about 0.05 mol % and about 3.0 mol %, and even
between about 0.05 mol % and about 1.0 mol % calcium oxide. In some
cases, the bond material powder can be essentially free of calcium oxide.

[0041] The amount of barium oxide within the bond material powder can be
limited, and particularly less than the content of magnesium oxide and/or
calcium oxide. For example, embodiments herein may utilize a bond
material powder formed from not greater than about 5.0 mol % barium
oxide, such as not greater than about 3.0 mol %, not greater than about
2.0 mol %, or even not greater than about 1.0 mol % barium oxide of the
total moles of the bond material powder. Notably, the bond material
powder can be formed from between about 0.01 mol % and about 5.0 mol %,
such as between about 0.05 mol % and about 3.0 mol %, and even between
about 0.05 mol % and about 1.0 mol % barium oxide. In some cases, the
bond material powder can be essentially free of barium oxide.

[0042] According to embodiments herein, the final vitreous bond material
can be formed from a bond material powder, which can be formed to have a
particular content of alumina (Al2O3). Notably, the bond
material powder can be formed from particularly high contents of alumina
to saturate the bond material during formation and reduce thermodynamic
potential of grain dissolution by the bond material. For example,
embodiments herein may utilize a bond material powder formed from an
amount of alumina of at least about 14 mol %, such as at least about 14.5
mol %, at least about 15 mol %, at least about 15.5 mol %, at least about
16 mol %, at least about 16.5 mol %, at least about 17 mol %, at least
about 18 mol %, at least about 19 mol %, or even at least about 20 mol %.
Still, the content of alumina may be limited, such that the bond material
powder composition contains between about 14 mol % and about 30 mol %,
between about 14 mol % and about 25 mol %, between about 14 mol % and
about 23 mol %, between about 14 mol % and about 20 mol %, between about
14 mol % and about 19 mol %, between about 14 mol % and about 18 mol %,
between about 15 mol % and about 18 mol %, or even between about 16 mol %
and about 18 mol % alumina.

[0043] In addition to the oxide species noted above, the final vitreous
bond may be formed from a bond material powder having a particular
content of phosphorous oxide (P2O5), which may be a
particularly small amount compared to certain low-temperature bond
compositions. For example, the bond material powder can be formed from
less than 1.0 mol % phosphorous oxide. In other embodiments, the bond
material powder can be formed from less than about 0.5 mol % phosphorous
oxide. In particular instances, the bond material powder can be formed
such that it is essentially free of phosphorous oxide.

[0044] Additionally, the bond material powder can be formed from
particular contents of boron oxide (B2O3). For example, the
bond material powder may be formed from at least about 5.0 mol %, at
least about 8.0 mol %, at least about 10 mol %, at least about 12 mol %,
or even at least about 15 mol % boron oxide. In certain instances, the
bond material powder can be formed from between about 5.0 mol % and about
25 mol %, such as between about 5.0 mol % and 20 mol %, between about 10
mol % and about 20 mol %, or even between about 12 mol % and about 18 mol
% boron oxide.

[0045] In addition to certain species noted above, additional metal oxide
compounds can be added to the mixture to facilitate the formation of the
final vitreous bond material. Some suitable additional compounds can
include oxides of transition metal elements, including for example, but
not limited to, zinc oxide, iron oxide, manganese oxide, titanium oxide,
chromium oxide, zirconium oxide, bismuth oxide and a combination thereof.
Each of the additional metal oxide compounds may be present in minor
amounts, such as not greater than about 5.0 mol %, not greater than about
3.0 mol %, or even not greater than about 1.0 mol %.

[0046] After making a mixture of abrasive grains and bond material powder,
it will be appreciated, that other materials may be added to the mixture.
For example, certain organic compounds may be added to the mixture such
as binders and the like to facilitate formation of the article. In
accordance with one particular embodiment, the mixture can contain a
certain content of polyethylene glycol, animal glue, dextrin, maleic
acid, latex, wax emulsion, PVA, CMC, and other organic and/or inorganic
binder.

[0047] Additionally, other additives may be provided within the mixture to
facilitate formation of the final-formed bonded abrasive article. For
example, some suitable additives can include pore formers including, but
not limited to, hollow glass beads, ground walnut shells, beads of
plastic material or organic compounds, foamed glass particles and bubble
alumina, elongated grains, fibers and combinations thereof. Other types
of filler materials can include inorganic materials, such as pigments
and/or dyes which can provide color to final formed abrasive article.

[0048] After forming the mixture at step 101, the process can continue at
step 103 by forming the mixture to form a green article. A green article
is reference to an unfinished article, which may not be thoroughly heat
treated to complete densification (i.e. fully sintered). In accordance
with one embodiment, the process of forming the mixture can include a
pressing operation wherein the mixture is pressed into a particular shape
similar to the shape of the intended final-formed bonded abrasive
article. A pressing operation may be conducted as a cold pressing
operation. Suitable pressures can be within a range between about 10 and
about 300 tons.

[0049] After suitably forming the mixture at step 103, the process can
continue at step 105 by heating the green article to form an abrasive
article having abrasive grains contained within a vitreous bond material.
The process of heating the green article can include heating the green
article in a furnace to a firing temperature of at least 800° C.
to form the abrasive article. Firing is generally carried out at a
temperature suitable to form a vitrified bond material as measured by the
set point of the furnace. The forming processes of the embodiments herein
may utilize notably high firing temperatures, such as at least about
825° C., at least about 850° C., at least about 875°
C., at least about 900° C., at least about 910° C., at
least about 950° C., at least about, at least about 1000°
C., at least about 1050° C., at least about 1100° C., at
least about 1150° C., at least 1200° C., at least about
1250° C., or even at least about 1300° C. The firing
temperature used to form the bonded abrasive articles of embodiments
herein can be within a range between about 800° C. and about
1400° C., such as within a range between about 800° C. and
about 1300° C., such as within a range between about 900°
C. and about 1400° C., such as within a range between about
900° C. and about 1300° C. or even within a range between
1100° C. and about 1400° C.

[0050] Generally, firing can be carried out in an ambient atmosphere, such
that it contains air. Generally, the duration of peak temperature for
firing can be at least about 1 hour, and particularly within a range
between about 1 to 10 hours. After sufficiently heating the article to
form a bonded abrasive article having abrasive grains contained within a
vitreous bond material, the article can be cooled. Embodiments herein may
utilize a natural and/or controlled cooling process.

[0051] The bonded abrasive articles of embodiments herein can include
abrasive grains contained within a bond material, wherein the bond
material is a vitreous material having an amorphous phase. It is noted
that particular contents of certain compositions (e.g. alkaline oxide
compounds, silica, alumina, boron oxide, etc), can change during the high
temperature forming process such that the final-formed bonded abrasive
article has a different content of such compositions as compared to the
content of such compositions within the initial mixture. The bonded
abrasive articles of embodiments herein are formed such that the final
bond material of the abrasive article has certain contents of certain
components, and particularly a content of alumina and particular ratios
of certain components to facilitate forming the abrasive article.

[0052] We now refer to certain aspects of the vitreous bond material in
the final-formed abrasive article. As will be appreciated, the bond
material of the final-formed abrasive article can contain a significant
amount of an amorphous phase, such that a majority of the bond material
comprises an amorphous phase. In fact, substantially all of the bond
material can contain an amorphous phase material such that the bond
material consists essentially of an amorphous phase. Still, it will be
appreciated that the bond material may contain some content of
crystalline phase, however, the amount of such crystalline phases is
generally a minority amount (i.e., less than about 50 vol % of the total
volume of the abrasive article).

[0053] The vitreous bond material can have a certain content of silica. In
accordance with one embodiment, the final-formed bond material can
contain not greater than about 70 mol % silica of the total moles of
material within the bond material. Other embodiments can contain a
different amount of silica in the final vitreous bond material, such as
not greater than about 65 mol %, such as not greater than about 60 mol %,
not greater than about 55 mol %, or even not greater than about 50 mol %.
Still, in certain embodiments, the bond material can have between about
30 mol % and about 70 mol % silica, between 35 mol % and about 65 mol %
silica, between about 35 mol % and about 60 mol % silica, and even
between about 40 mol % and about 50 mol % silica.

[0054] The final-formed bond material of embodiments herein can have a
particular content of boron oxide. For example, the final-formed bond
material can have at least about 5.0 mol % boron oxide of the total moles
in the bond material. In other instances, the bond material can contain
at least about 8.0 mol %, such as at 10 mol %, such as at least about 15
mol % boron oxide. In certain embodiments, the bond material has a
content of boron oxide within a range between about 5.0 mol % and about
30 mol %, such as between about 10 mol % and about 25 mol %, or even
between about 12 mol % and about 18 mol %.

[0055] The final-formed bond material can exhibit certain contents of
alumina (Al2O3) suitable for forming the high-temperature
bonded abrasive article of embodiments herein. For example, the total
content of alumina within the vitreous bond material can be at least
about 15 mol %, such as at least about 15.5 mol %, at least about 16 mol
%, at least about 16.5 mol %, or even at least about 17 mol %. Certain
abrasive articles can have a total content of alumina within the vitreous
bond material within a range between about 15 mol % and about 25 mol %,
such as between about 15.5 mol % and about 22 mol %, and about 16 mol %
and about 20 mol %.

[0056] Notably, the vitreous bond material can have a particular ratio of
alumina as compared to other species within the bond material, including
for example, but not limited to silica. The vitreous bond material can
have a ratio of a total content of alumina [C.sub.Al2O3] in mol % as
compared to a total content of silica [C.sub.SiO2] in mol %, wherein the
ratio of [C.sub.Al2O3]/[C.sub.SiO2] is at least about 0.2. In certain
other embodiments, the ratio [C.sub.Al2O3]/[C.sub.SiO2] can be at least
about 0.3, such as at least about 0.35, at least about 0.4, at least
about 0.5, or even at least about 0.6. In particular instances, the ratio
[C.sub.Al2O3]/[C.sub.SiO2] can be within a range between about 0.2 and
about 1, such as between about 0.3 and about 0.9, between about 0.4 and
about 0.8, between about 0.3 and about 0.7, and even between about 0.3
and about 0.6.

[0057] Moreover, the vitreous bond material can contain a particular ratio
between the amount of alumina and the amount of boron oxide. For example,
the vitreous bond material can have a ratio between the total content of
alumina [C.sub.Al2O3] in mol % and the total content of boron oxide
[C.sub.B2O3] in mol %, described as [C.sub.Al2O3]/[C.sub.B2O3] that can
be within a range between about 0.2 and about 2. In other instances, the
ratio [C.sub.Al2O3]/[CB2O3] can be within a range between about 0.5
and about 2, such as between about 0.5 and about 1.5, such as between
about 0.8 and about 1.5, between about 0.8 and about 1.3, and even
between about 0.9 and about 1.2.

[0058] According to certain embodiments herein, the vitreous bond material
of the abrasive article can be formed of a particular composition to
mitigate abrasive grain dissolution during forming processes. In
particular, the vitreous bond material can be formed from a powder bond
material having a sufficient amount of alumina to reduce the dissolution
of abrasive grains into the bond material. The degree of dissolution can
be measured by a change in total alumina content [Δ
Al2O3] between the alumina content of the powder bond material
[PBM.sub.Al2O3] and the total alumina content of the vitreous bond
material [VBM.sub.Al2O3]. Certain abrasive articles according to
embodiments herein can have a change in total alumina content of not
greater than about 15.0 mol % as calculated by the equation [Δ
Al2O3]=([VBM.sub.Al2O3-PBM.sub.Al2O3]/[PBM.sub.Al2O3]. In other
embodiments, the change in total alumina content can be less, such as not
greater than about 12.0 mol %, not greater than about 10.0 mol %, not
greater than about 8.0 mol %, not greater than about 6.0 mol %, not
greater than about 5.0 mol %, not greater than about 3.0 mol %, or even
not greater than about 1.0 mol %. According to at least one embodiment,
the change in total alumina content is within a range between about 0.01
mol % and about 15.0 mol %, such as between about 0.5 mol % and about 12
mol %, between about 1.0 mol % and about 12 mol %, between about 1/0 mol
% and about 10 mol %, and even between about 1.0 mol % and about 8.0 mol
%.

[0059] The abrasive articles of embodiments herein can have a total
content of alkali oxide compounds within the bond material. That is, the
total amount of alkali oxide compounds [Caoc] within the final bond
material can be not greater than about 15 mol %. In particular, the total
content of alkali oxide compounds can be not greater than about 12 mol %,
not greater than about 11 mol %, not greater than about 10 mol %, not
greater than about 8.0 mol %, not greater than about 6.0 mol %, or even
not greater than about 5.0 mol %. In certain instances, the abrasive
articles herein are formed such that the bond material has a total
content of alkali oxide compounds within a range between about 1.0 mol %
and about 15 mol %, such as between about 1.0 mol % and about 15 mol %,
between about 2.0 mol % and about 10 mol %, between about 2.0 mol % and
about 8.0 mol %, or even between about 2.0 mol % and about 5.0 mol %.

[0060] As noted above, the initial mixture of the bond material powder
used to form the final vitreous bond material can contain particular
amounts of certain alkali oxide compounds such as sodium oxide. As such,
the vitreous bond material of the abrasive article can have at least
about 2.0 mol % sodium oxide. In other bond materials, the amount of
sodium oxide can be at least about 5.0 mol %, at least about 6.0 mol %,
at least about 8.0 mol %, and particularly within a range between about
2.0 mol % and about 20 mol %, between about 4.0 mol % and about 18 mol %,
at least about 6.0 mol % and about 16 mol %, at least about 8.0 mol % and
about 15 mol %. Notably, the amount of sodium oxide within the final
vitreous bond material can be greater than the amount of any other alkali
oxide compounds, such as potassium oxide or lithium oxide. In fact,
certain vitreous bond materials can have an amount of sodium oxide that
is greater than the total content of potassium oxide and lithium oxide
combined.

[0061] The vitreous bond material can have an amount of potassium oxide
present in a minor amount. For example, the vitreous bond material can
include not greater than about 5.0 mol % potassium oxide, such as not
greater than about 3.0 mol % potassium oxide, not greater than about 2.5
mol % potassium oxide, or even not greater than about 2.0 mol % potassium
oxide. Certain embodiments may utilize an amount of potassium oxide
within a range between about 0.01 mol % and about 5.0 mol %, such as
between about 0.1 mol % and about 3.0 mol %. Notably, in some embodiments
the final-formed bond material of the abrasive article can be essentially
free of potassium oxide.

[0062] The vitreous bond material can have an amount of lithium oxide that
is low, particularly lower than amounts of sodium oxide or potassium
oxide. For example, the vitreous bond material can include not greater
than about 5.0 mol % lithium oxide, such as not greater than about 3.0
mol % lithium oxide, not greater than about 2.5 mol % lithium oxide, or
even not greater than about 2.0 mol % lithium oxide. Certain embodiments
may utilize an amount of lithium oxide within a range between about 0.01
mol % and about 5.0 mol %, such as between about 0.1 mol % and about 3.0
mol %. Notably, in some embodiments the final-formed bond material of the
abrasive article can be essentially free of lithium oxide.

[0063] Moreover, the vitreous bond material can contain a particular ratio
between the amount of alumina and the total amount of alkali oxide
compounds. For example, the vitreous bond material can have a ratio
between the total content of alumina [C.sub.Al2O3] in mol % and the total
content of alkali oxide compounds [Caoc] in mol %, described as
[C.sub.Al2O3]/[Caoc] that can be at least about 0.8. In other
embodiments, the value of the ratio can be greater, such as at least
about 0.85, at least about 0.9, at least about 1.0, at least about 1.05,
or even at least about 1.1. Particular embodiments can utilize a ratio
having a value within a range between about 0.8 and about 2.5, such as
between about 0.8 and about 2.2, between about 0.8 and about 2.0, between
about 0.9 and about 1.8, between about 0.8 and about 1.5, between about
0.9 and about 1.4, between about 0.95 and about 1.35, between about 1.0
and about 1.3, or even between about 1.1 and about 1.25.

[0064] Additionally, the final-formed bond material may contain a certain
content of alkaline earth oxide compounds [Caeoc]. In particular
instances, the abrasive article can be formed such that the vitreous bond
material can contain not greater than about 15 mol %, such as not greater
than about 12 mol %, not greater than about 10 mol %, not greater than
about 8.0 mol %, not greater than about 5.0 mol %, or even not greater
than about 3.0 mol % alkaline earth oxide compounds. According to certain
embodiments, the bond material can have a total content of alkaline earth
oxide compounds between about 0.5 mol % and about 15 mol %, between about
1.0 mol % and about 10 mol %, between about 1.0 mol % and about 8.0 mol
%, and even between about 1.0 mol % and about 5.0 mol % alkaline earth
oxide compounds.

[0065] The vitreous bond material may contain specific amounts of alkaline
earth oxide compounds. For example the vitreous bond material can contain
a greater content of magnesium oxide than the content of barium oxide. In
fact, the content of magnesium oxide within the vitreous bond material
can be greater than the content of calcium oxide. More particularly, the
content of magnesium oxide can be greater than the content of barium
oxide and calcium oxide combined. Particular vitreous bond materials can
contain an amount of magnesium oxide within a range between about 0.2 mol
% and about 5.0 mol %, such as between about 0.5 mol % and about 3.0 mol
%, and even between about 0.5 mol % and about 2.0 mol %. Certain vitreous
bond materials may be essentially free of calcium oxide and/or barium
oxide.

[0066] The bond may contain minor amounts of other materials, particularly
oxide compounds, such as phosphorous oxide. For example, the final-formed
bond material can have less than about 1.0 mol % of phosphorous oxide,
such as less than about 0.5 mol % phosphorous oxide. In particular, the
final-formed bond material of the abrasive article can be essentially
free of phosphorous oxide.

[0067] The abrasive articles according to embodiments herein can contain a
total abrasive grain content of at least about 34 vol % of the total
volume of the abrasive body. For example, the abrasive grain content
within the abrasive body can be at least about 38 vol %, at least about
40 vol %, at least about 42 vol %, at least about 44 vol %, at least
about 46 vol %, or even at least about 50 vol %. In particular instances,
the abrasive grain content can be within a range between about 34 vol %
to about 60 vol %, such as between about 34 vol % and about 56 vol %,
between about 40 vol % and about 54 vol %, and particularly between about
44 vol % and about 52 vol % of the total volume of the abrasive article.
The MCA abrasive can account for between about 1 to about 100 vol % of
the total abrasive grains of the abrasive article, such as between about
10 vol % and about 80 vol %, or between 30 vol % and about 70 vol % of
the total volume of abrasive grains in the abrasive article. Moreover,
some abrasive articles can include 0.1 vol % to 60 vol % of one or more
secondary abrasive grains, fillers and/or additives.

[0068] The abrasive articles of the embodiments herein can include at
least about 4 vol % vitreous bond material for the total volume of the
abrasive body. In particular instances, the abrasive body can contain at
least about 5 vol % bond, at least about 6 vol % bond, at least about 7
vol % bond, or even at least about 8 vol % bond. In certain abrasive
articles, the abrasive body can contain between about 4 vol % and about
30 vol % bond material, such as between about 4 vol % and about 25 vol %
bond, between about 5 vol % and about 20 vol % bond, and even between
about 6 vol % to about 12 vol % bond.

[0069] While a majority of the abrasive tools can have various degrees of
porosity, some of the abrasive bodies formed according to embodiments
herein may exhibit a certain content of porosity. For example, the
abrasive body can have a porosity that is at least about 30 vol % of the
total volume of the abrasive article. In other instances, the porosity
can be greater, such as at least about 35 vol %, at least about 40 vol %,
or even at least about 45 vol %. Particular abrasive articles can have a
content of porosity within a range between about 30 vol % and about 50
vol %, such as between about 30 vol % and about 45 vol %, and more
particularly between about 35 vol % and about 45 vol %.

[0070] The abrasive articles of the embodiments herein demonstrate
suitable levels of abrasive grain integrity, as measured by the attack of
the bond material on the abrasive grains during a forming process.
Abrasive articles formed according to embodiments herein were studied for
abrasive grain dissolution, which was measured on samples of
approximately 48 vol % abrasive grains of microcrystalline alumina,
approximately 10 vol % bond material, and approximately 42 vol %
porosity. The abrasive grain dissolution was recalculated based on the
difference between the initial and the final alumina content of the bond.
The final bond composition was measured by microprobe analysis using an
SX50 machine available from CAMECA Corporation. An average of at least 10
analytical points in the bond with a spot size of 10 microns was used for
each of the measurements, which was then averaged for each sample.

[0071] The abrasive articles of embodiments herein demonstrated a grain
dissolution factor, as measured according to the test conditions provided
above, of not greater than about 1.5 wt %. Some abrasive articles of the
embodiments herein demonstrated a grain dissolution factor of not greater
than about 1.2 wt %, not greater than about 1.1 wt %, not greater than
about 1.0 wt %, about 0.9 wt %, such as not greater than about 0.8 wt %,
not greater than about 0.7 wt %, not greater than about 0.5 wt %, or even
not greater than about 0.4 wt %. Still, certain embodiments demonstrate a
grain dissolution factor within a range between about 0.01 wt % and about
1.5 wt %, such as between about 0.01 wt % and about 1.3 wt %, between
about 0.01 wt % and about 1.2 wt %, between about 0.01 wt % and about 1.1
wt %, between about 0.01 wt % and about 1.0 wt %, between about 0.01 wt %
and about 0.9 wt %, between about 0.05 wt % and about 0.8 wt %, or even
between about 0.1 wt % and about 0.8 wt %.

EXAMPLES

Example 1

[0072] A series of samples were prepared, including 5 samples (Samples S1,
S2, S3, S4 and S5) formed according to embodiments herein and 5
conventional samples (Samples CS1, CS2, CS3, and CS4) having a
conventional bond. The grain dissolution factor was tested for each of
the samples and is set forth below.

[0073] The samples S1-S5 were formed by initially combining 80-90 wt % of
abrasive grains with 9-15 wt % of an initial bond material having the
amounts of alumina indicated in Table 1 below. The samples S1-S5 were
initially cold pressed to form a green article, and thereafter sintered
at a firing temperature of about 950° C., 1000° C. or
1050° C. to form a final bonded abrasive article having
approximately 46-50 vol % abrasive grains, 7-12 vol % vitreous bond
material, and a reminder amount of porosity. The final content of alumina
within the bond material was measured via microprobe analysis using an
SX50 machine available from CAMECA Corporation.

[0074] The conventional samples CS1-CS4 were formed according to the same
processes of samples S1-S5, and the initial alumina content within the
bond for each of the conventional samples is provided in Table 1 below.
The final content of alumina within the bond material was measured via
microprobe analysis using an SX50 machine available from CAMECA
Corporation.

[0075] After forming all of the samples the grains dissolution factor was
measured for each sample based on the equations provided below, wherein
each of the variables (e.g., mGi) are indicated in Table 1. It should be
noted that for the calculation, it is assumed that all the alumina
enrichment comes from alumina grain dissolution. The amount of alumina
enrichment is then recalculated as grain loss in wt %, taking into
account the density of the alumina grain, and the density of the initial
bond, which was measured via helium pycnometry.

[0076] As illustrated by the data of Table 1 below, each of the samples
S1-S5 had a grain dissolution factor, as demonstrated by the value of the
alumina grain loss in weight percent that is significantly less than the
grain dissolution factor of the conventional samples CS1-CS4. Each of the
samples S1-S5 demonstrated a greater content of initial alumina and a
change in alumina content between the initial alumina content and the
final alumina content that was significantly less than the conventional
samples CS1-CS4. While the mechanism is not fully understood, the data
suggests that certain contents of alumina within the initial bond
material may limit grain dissolution. Moreover, without wishing to be
tied to a particular theory, it is suspected that other factors may
contribute to limiting the grain dissolution, including for example, the
content of certain compounds, such as boron oxide, alkali oxide
compounds, alkaline earth oxide compounds, and the like.

[0077] Two samples are formed. Sample S6 is formed according to the
embodiments herein. Sample CS5 is a conventional sample having the same
characteristics of Sample CS1 of Example 1. Notably, samples S6 and CS5
have the same structure as samples of Example 1, however, the samples are
fired at 915° C.

[0078] Sample S6 has a starting alumina weight percent of 26.94 wt %
(18.59 mol %) and a final alumina content of 28.7 wt % (19.25 mol %),
thus demonstrating an alumina grain dissolution of 0.33 wt % as measured
according to the methods disclosed herein. Sample CS5 has a starting
alumina content of 16.05 wt % (10.13 mol %), a final alumina content of
25.5 wt % (17.02 mol %), and thus an alumina grain dissolution of 1.70 wt
%, as measured according to the formula and methods described herein. As
such, sample S6 demonstrates significantly less alumina grain dissolution
during the forming process.

[0079] The samples S6 and CS5 were subject to an internal diameter
grinding operation to determine the power consumption of the bonded
abrasive articles per grinding cycle and also the straightness of the
samples S6 and CS5 after the grinding procedure. The grinding conditions
are summarized in Table 2 below.

[0080] FIGS. 2 and 3 summarize the test results. FIG. 2 includes a plot of
power versus number of grinding cycles for each of the samples (i.e., S6
and CS5). The data of FIG. 3 demonstrates that the sample S6 utilizes
less power for all grinding cycles, and thus a lower average power
consumption for each of the grinding cycles, suggesting that sample S6
has improved abrasive grain integrity as compared to sample CS5.

[0081] Additionally, FIG. 3 includes a plot of straightness versus number
of grinding cycles, which is a measure of the linearity of the surface
generated in the workpiece after the grinding operation by the bonded
abrasive article. The straightness of the part generated can be related
to the uniformity of wheel wear in the edges and the bulk regions.
Straightness measurements are performed with the help of a round gage
(Formscan 260 from Mahr Federal) and line profiles are generated along
the surface of the workpiece. Four such measurements are made on each
part and their average is reported as the value of straightness. This
test method is according to the standard ASME Y14.5M "Dimensioning and
Tolerancing." As illustrated, the sample S6 demonstrates approximately
the same degree of variation in the straightness as compared to sample
CS5. As such, in conjunction with the data of FIG. 2, sample S6 is
capable of delivering the same quality grinding performance while using
less power, thus providing a more efficient grinding process as compared
to sample CS5.

[0082] The embodiments herein are directed to abrasive articles
incorporating microcrystalline alumina grains in a high temperature
bonded abrasive article, wherein the microcrystalline alumina grains
exhibit improved integrity and minimized dissolution and degradation.
Generally, the state-of-the-art bonded abrasive articles employing MCA
grains have been directed to the formation and use of low temperature
vitrified bonds formed at temperatures below 1000° C. However, the
embodiments herein are directed to a bonded abrasive article formed to
include certain contents (e.g., ratio) of materials within the bond
material powder, to form vitreous bond compositions capable of being
formed at high temperatures while mitigating the degradation and/or
dissolution of the abrasive grains comprising MCA during forming. The
embodiments herein can utilize one or more combinations of features,
including particular bond compositions, particular ratios of compounds
within the bond, including but not limited to, a ratio between the
alumina and silica, a ratio between the alumina and boron oxide, a ratio
between the alumina and alkali oxide compounds, as well as ratios between
other components including boron oxide, alkaline earth oxides, alkali
oxide compounds, and the like. The foregoing describes a combination of
features, which can be combined in various manners to describe and define
the bonded abrasive articles of the embodiments. The description is not
intended to set forth a hierarchy of features, but different features
that can be combined in one or more manners to define the invention.

[0083] In the foregoing, reference to specific embodiments and the
connections of certain components is illustrative. It will be appreciated
that reference to components as being coupled or connected is intended to
disclose either direct connection between said components or indirect
connection through one or more intervening components as will be
appreciated to carry out the methods as discussed herein. As such, the
above-disclosed subject matter is to be considered illustrative, and not
restrictive, and the appended claims are intended to cover all such
modifications, enhancements, and other embodiments, which fall within the
true scope of the present invention. Thus, to the maximum extent allowed
by law, the scope of the present invention is to be determined by the
broadest permissible interpretation of the following claims and their
equivalents, and shall not be restricted or limited by the foregoing
detailed description.

[0084] The Abstract of the Disclosure is submitted with the understanding
that it will not be used to interpret or limit the scope or meaning of
the claims. In addition, in the foregoing Detailed Description, various
features may be grouped together or described in a single embodiment for
the purpose of streamlining the disclosure. This disclosure is not to be
interpreted as reflecting an intention that the claimed embodiments
require more features than are expressly recited in each claim. Rather,
as the following claims reflect, inventive subject matter may be directed
to less than all features of any of the disclosed embodiments. Thus, the
following claims are incorporated into the Detailed Description, with
each claim standing on its own as defining separately claimed subject
matter.